4-甲基辛酸的简易合成

以4-甲基环己酮为原料,简易地合成了重要香原料4-甲基辛酸。首先用4-甲基环己酮与乙醛(摩尔比1.07∶1)在w(NaOH)=1%的水溶液作用下,于5～10℃反应得到的Aldol缩合产物,经磷酸于100℃减压脱水和w(Pd)=5%的Pd/C催化选择性加氢生成4-甲基-2-乙基环己酮,产率37.2%;再用CrO3/硫酸于25℃氧化开环生成4-甲基-6-氧代辛酸,产率87.9%;最后用Wolff-Kishner-黄鸣龙还原反应脱去羰基,得到质量分数为99.3%的4-甲基辛酸,产率58.4%。所得产物的结构经IR、1HNMR、13CNMR、GC-MS表征。

Facile Synthesis of 4-Methyloctanoic Acid

4-methyloctanoic acid is an important flavoring substances.It was prepared from the starting material 4-methylcyclohexanone.Firstly,4-methylcyclohexanone condensated with acetaldehyde(mol ratio=1.07∶1)over w(NaOH)=1% aqueous solution at 5～10 ℃.The aldol condensation product was dehydrated by phosphoric acid under reduced pressure at 100 ℃ and then hydrogenated by Pd/C〔w(Pd)=5%〕 catalyst,4-methyl-2-ethylcyclohexanone was obtained in 37.2% yield;Secondly,4-methyl-2-ethylcyclohexanone was oxidated to open the ring by CrO3/H2SO4,4-methyl-6-oxooctanoic acid was obtained in 87.9% yield;Finally,4-methyloctanoic acid was obtained through decarbonylation by Huang Minlon Reduction in 58.4% yield(mass fraction 99.3% pure).Their structures were characterized by IR、1HNMR、13CNMR、GC-MS.